The effect of single-prong high-flow nasal cannula therapy on CO 2 clearance

Abstract

Background

High-flow nasal cannula therapy has multiple proposed benefits, one of which is the clearance of exhaled CO₂ from the upper airway. The removal of exhaled CO₂ is made more difficult when the patient has a closed or partially closed mouth, as this removes or restricts the primary escape route for CO₂-laden exhaled flow. It is proposed that this increased flush difficulty could be partially alleviated by using a single-prong cannula design, therefore allowing exhaled flow to be evacuated out of the open naris.

Methods

Unsteady simulations were run to investigate the effect that the proposed single-prong high-flow therapy has on CO₂ flush at intermediate and high flush difficulty scenarios. Single- and dual-prong geometries were tested under identical conditions including simulated mouth opening, respiratory cycle, airway geometry, and therapy flow setting. Therapy flows tested with both cannula geometries ranged from 12 to 45 L/min. All data discussed in this study was collected from computational models.

Results

The single-prong geometry resulted in less CO₂ inhalation when all other factors were equal. The distinction between cannula geometries grew as therapy flow was decreased and as the mouth opening was decreased. Pathlines, colored by residence time in the upper airway, were released from the trachea. The pathlines showed longer expiratory flow residence times in the airway for the dual-prong cannula, reinforcing the notion that that the single-prong cannula improves the efficiency of expiratory flow removal.

Conclusions

The results can be used to provide a framework for clinical studies investigating the potential benefits of single-prong cannulas. This would be particularly important in difficult-to-flush scenarios such as when the patient’s mouth is fully closed.

Quick look

Current knowledge

High-flow nasal cannula therapy has multiple proposed benefits, one of which is the minimization of rebreathing CO₂-rich exhaled flow due to the flushing effect imposed by the therapy flow. This mechanism of action has been found to be dependent on numerous factors such as cannula prong diameter, therapy flow, and patient mouth opening. It is hypothesized that the flush effect is hindered at lower patient mouth openings due to the restriction of the main evacuation point for exhaled flow. Recent studies have shown that an asymmetric cannula design, in which one prong has a larger diameter than the other, can enhance CO₂ flush.

What this paper contributes to our knowledge

Based on the previous work examining asymmetric cannula designs for high-flow therapy, it was hypothesized that a single-prong cannula design, in which one naris is left completely open, would assist CO₂ flush in difficult-to-flush scenarios. The single-prong cannula resulted in lower CO₂ inhalation than a dual-prong cannula with a partially open (20%) and completely closed simulated patient mouth if all other factors (therapy flow, breath cycle, and airway geometry) were held constant. The distinction between the cannula geometries was larger with a closed mouth than with a partially open mouth. The residence time of expiratory flow in the upper airway was examined, and it was found that the single-prong geometry resulted in a lower residence time (or quicker evacuation of exhaled flow) than the dual-prong geometry.

Introduction

High-flow nasal cannula (HFNC) therapy emerged around the year 2000 as a new modality for the management of acute and chronic respiratory failure. Unlike conventional oxygen delivery systems, HFNC provides heated, humidified oxygen at flows that meet or exceed patient inspiratory demand, improving oxygenation and reducing the work of breathing. Physiological benefits include enhanced carbon dioxide (CO₂) clearance, mild positive airway pressure, and improved secretion mobilization, making HFNC suitable for diverse clinical scenarios such as hypoxemic respiratory failure, post-extubation support, and palliative care settings.^1–4

Recent technological advancements have focused on optimizing HFNC systems for efficiency, patient comfort, and resource conservation. Traditional dual-prong cannulas, while effective, ⁵ often require high flows (up to 60 L/min) to achieve therapeutic goals, which use more oxygen and limit portability in home care or transport settings. ⁶ Previous work by the authors revealed that CO₂ flush from the upper airway by traditional two-prong HFNC is reduced when the mouth is closed. ⁷ These limitations would benefit from design refinements that would enhance CO₂ flush. In a randomized controlled trial, Boscolo et al tested an asymmetric cannula design, in which one of the nasal prongs has a larger diameter, against a standard interface and measured end-expiratory lung impedance, diaphragm ultrasound thickening fraction and excursion, ventilatory efficiency, gas exchange, dyspnea, and patient comfort. The authors determined that all factors other than patient comfort were not significantly different, while patients reported improved comfort when using the asymmetrical interface. ⁸ Tatkov et al used bench top experiments and mathematical modeling to find that the efficiency of CO₂ clearance could be improved using an asymmetrical cannula design. ⁹

Clinical evaluations suggest that single-prong HFNC therapy achieves comparable dyspnea relief and CO₂ clearance at median flows of 15 L/min versus 25 L/min for dual-prong systems, offering significant oxygen conservation benefits. ¹⁰ This design also provides practical advantages for patients with facial trauma, cleft palate, or nasogastric tubes, where traditional cannulas may be contraindicated. Additionally, the ability to alternate nostril placement reduces irritation and enhances long-term tolerance.

Given the growing emphasis on patient-centered care and resource optimization, single-prong HFNC therapy represents a promising alternative to conventional HFNC systems. However, evidence regarding its clinical efficacy, patient comfort, and impact on oxygen utilization remains limited. This study aims to compare single- and dual-prong HFNC interfaces using a computational model of an adult upper airway.

Methods

All data discussed in this study was collected from computational models. The simulations were composed of an upper airway that was reconstructed from computerized tomography (CT) scans, one of two nasal cannula geometries, and an environment zone designed to accommodate the simulated breath mixing outside the airway (see Figure 1). The CT scans were collected with a 0.55 mm resolution and 2 mm slice thickness from a 71.6-inch tall, 205-pound, 27-year-old man. Linear interpolation of the 2 mm slices was used to achieve a 0.5 mm effective slice thickness. The CT scans were collected as part of a prior study, which was approved by Liberty University’s Institutional Review Board (IRB) with the approval number IRB-FY20-21-313. The dual-prong cannula had a prong inner diameter of 2.95 mm, while the single-prong cannula had a prong inner diameter of 4.17 mm. When considering the number of prongs for each geometry, the different cannula geometries result in a 0.0925% difference in total prong exit area. This means that the same therapy flow being administered with each cannula geometry will result in roughly the same therapy velocity. The outlet from the environment zone is hidden in Figure 1 to give an unobstructed view of the face and nasal cannula geometry. The simulated mouth opening was modified to different percentages by changing the setting of various mouth open ellipses, which can also be seen in Figure 1. The mouth open ellipses were divided from an interface in the oral cavity near the teeth; this interface was considered the boundary between the airway and the environment. The ellipses were specified such that they relate to targeted percentages of the overall area of the interface. For example, if the mouth was to be set to 5% open, the smallest inner ellipse would be set to an invisible face, which allows flow to freely pass through it, and the rest of the interface would be set to walls. The primary analysis for this study included a 20% open simulated mouth, and a secondary analysis included a fully closed simulated mouth.

Figure 1.

Views of the airway geometry with face shown (left) and face hidden (middle). A closeup of the interface used to set the mouth open percent is shown (lower right), along with closeups of the two cannula geometries tested (upper right).

Simulations were carried out using ANSYS Fluent 2022R1, a commercially available computational fluid dynamics (CFD) solver that works by satisfying governing equations, such as momentum balance, within a simulated domain (more information on the governing equations can be found in the supplemental material). The domain is broken down into many smaller elements, which are collectively known as a computational mesh. The governing equations are then solved within those elements to define the fluid (liquid and/or gas) flow within the domain at a given moment in time. For unsteady models, this solution process is repeated at pre-defined intervals, known as timesteps, to compute the temporal governing equations of flow within the domain.

The simulation methodologies were validated using experimental data collected using an ASL5000 breathing simulator and a 3D printed human airway matching the geometry shown in Figure 1. Common practices used to ensure the accuracy of CFD models, such as mesh independence studies and timestep independence studies, were carried out as well. The validation process was published in a previous work by the authors. ¹¹ A realistic breathing curve was applied to the model via a temporally varying velocity boundary condition at the base of the trachea. The boundary condition prescribed velocity and gas species concentrations at the boundary each timestep. The gas species concentrations of flow entering the lungs (which were not simulated) were tracked during inhalation, and a surrogate of cellular respiration was used to convert O₂ to CO₂ before the expiratory phase began each breath cycle. O₂ was converted to CO₂ each expiratory phase until a CO₂ mass fraction of 0.07 was satisfied in the expiratory flow. This ensured standardized CO₂ exhalation conditions in each breath cycle regardless of previous breaths’ washout performance. Final values reported from the simulations were collected from models that had long reached quasi-steady state (QSS), a state in which certain statistical measures stop varying significantly with time. The specification of QSS allowed the authors to determine when enough data had been collected from the dynamically breathing model. Figure 2 shows mass CO₂ remaining in the airway versus time for numerous breath cycles, each of period 2.5 s. The final three breath cycles for two different simulations are overlaid to show the relatively minor variation between breath cycles. The breath cycle consists of an inspiratory phase (0 to ∼1.25 s) and an expiratory phase (∼1.25 to 2.5 s). Each breath cycle shown in Figure 2 has been temporally aligned to ensure that the same parts of each breath cycle correspond to the same time. End-exhalation occurs at a time of 2.5 s. The variation between breath cycles is particularly indistinguishable during the inspiratory phase and the latest stages of the expiratory phase, which are indicators of the amount of CO₂ inhaled. Note that measures other than the mass CO₂ remaining in the airway, such as local velocity and local species concentrations collected at a point monitor, were also considered when evaluating QSS.

Figure 2.

Instantaneous CO₂ remaining in the airway versus time plotted over a complete breath cycle. Both models shown were administered therapy at a therapy flow of 35 L/min, with the only difference being the cannula geometry used. Multiple breath cycles are overlaid to show the relatively small breath-to-breath variability for each model. End-exhalation occurs at a time of 2.5 s.

Results

Pathlines, which trace the flow path of the fluid and are colored by residence time, were released from the airway inlet in the trachea and are shown in Figure 3. Residence time in this context reflects the time that a fluid particle has spent in the airway, beginning at zero when it enters the airway at the base of the trachea. Note that there are not actually aerosolized particles in the simulated airway; the pathlines are simply tracking imaginary, massless particles to provide a visualization of the gas flow. However, the pathlines could theoretically be representative of aerosolized droplets in the airway if the droplets had a low enough Stokes number such that their trajectories would match those of their surrounding gas molecules. Images of the pathlines were collected from a right-profile view and a face-on view for each cannula geometry. The face and airway were left partially visible to give the reader a better understanding of where in the airway the pathlines are traversing.

Figure 3.

Pathlines released from the airway inlet are shown colored by residence time. The pathlines were collected at peak exhalation, and all images shown were collected from models being administered 35 L/min of therapy flow. The airway and face are partially opaque to give the reader a better understanding of where the pathlines are in the airway. The first row shows pathlines collected from models being administered therapy using a dual-prong cannula. The second row shows pathlines collected from models being administered therapy using a single-prong cannula. The left column shows a profile view, and the right column shows a face-on view.

Additional insights can be drawn from real-time flow animations of overhead views of the dual-prong and single-prong scenarios, respectively, in these two embedded URLs: dual https://youtu.be/MWptMZJILXU, single https://youtu.be/o6Rr3gf75w0. Imaginary massless particles were released from the CFD cannula inlet to track the traversal of therapy flow. They are colored by mass fraction of CO₂ using the same colorbars as in Figure 3. What is revealed is a more consistently penetrating therapy flow from the single-prong design, which culminates in a more predictable flow; therapy gas enters via one naris, mixes with expiratory flow (indicated by imaginary particles changing colors) in the nasopharynx, and then exits the open naris. On the other hand, the dual-prong therapy flow can be seen stagnating against the oncoming expiratory flow, reversing direction, and then exiting the nares without sufficiently mixing with the expiratory flow (as indicated by a less-pronounced color change for the imaginary particles). Note that this analysis was conducted at peak exhalation, and the discussed phenomena are assumed to be dependent on factors such as expiratory flow and airway geometry.

Figure 4 shows the instantaneous CO₂ remaining in the airway versus time for a complete breath cycle. The breath cycles are temporally aligned the same way as in Figure 2. The dual-prong models (solid lines) show consistently higher CO₂ retention throughout the breath cycle than their single-prong (dashed lines) counterparts. The disparity between cannula geometries is higher for the 12 L/min therapy flow than the 45 L/min therapy flow.

Figure 4.

Instantaneous CO₂ remaining in the airway versus time for a complete breath cycle. Two cannula geometries and two therapy flow settings are shown, with different colors indicating different therapy flow settings and different line styles indicating different cannula geometries. End-exhalation occurs at a time of 2.5 s.

Figure 5 shows ΔCO₂ versus time for a complete breath at five different therapy flow settings. The formulation of the ΔCO₂ metric is shown in equation (1):

$\mathrm{\Delta }{\text{CO}}_2={\left({\text{CO}}_2\right)}_{\text{dual}}-{\left({\text{CO}}_2\right)}_{\text{single}}$

(1)

where (CO₂)_dual is the instantaneous CO₂ remaining with a dual-prong cannula and (CO₂)_single is the instantaneous CO₂ remaining with a single-prong cannula. A positive ΔCO₂ value indicates that the single-prong cannula is resulting in greater CO₂ flush (less CO₂ remaining) than the dual-prong cannula at that instant in the breath cycle. A positive value of ΔCO₂ at end-exhalation, which occurs at a time of 2.5 s, is indicative of a scenario in which more CO₂ is likely to be inhaled if receiving therapy from a dual-prong cannula. Notice that the end-exhalation ΔCO₂ values are all positive, with the magnitude of ΔCO₂ at end-exhalation increasing as therapy flow decreases.

Figure 5.

Instantaneous ΔCO₂ remaining in the airway versus time for a complete breath cycle. ΔCO₂ was calculated by subtracting the CO₂ remaining in the airway using a single-prong cannula geometry from the CO₂ remaining in the airway using a dual-prong cannula geometry at a given time. Therefore, a positive ΔCO₂ value indicates that the single-prong cannula is resulting in greater CO₂ flush than the dual-prong cannula at the given therapy flow. End-exhalation occurs at a time of 2.5 s.

Figure 6 shows the mass of CO₂ inhaled each breath cycle versus therapy flow for the single-prong and dual-prong cannula geometries. The amount of CO₂ inhaled was calculated using instantaneous CO₂ data throughout the breath cycle. The mass of CO₂ remaining at the end of the inspiratory phase was subtracted from the mass of CO₂ remaining at the end of the expiratory phase. The bulk flow direction during this period was in through the nares and mouth and out through the trachea. Any small amount of CO₂ that left the airway via the mouth or nares during the inspiratory phase was considered negligible for the purposes of this calculation. The validity of the stated assumptions can be examined via the supplementary animations provided of the CO₂ concentration throughout a complete breath cycle for two of the models examined in this study (one single-prong and one dual-prong). These animations support the assumption that the amount of CO₂ that escapes the airway via the mouth and nares while the simulated subject is inhaling is negligible compared to the amount of CO₂ leaving the airway via the tracheal boundary. The single-prong cannula consistently results in less CO₂ inhalation than the dual-prong cannula for a given therapy flow.

Figure 6.

Cumulative mass CO₂ inhaled each breath cycle versus therapy flow.

Tabulated values of mass CO₂ inhaled for all models run during this study can be seen in Table 1. Models receiving therapy using a single-prong cannula geometry consistently inhaled less CO₂ than models receiving therapy using a dual-prong cannula if all other factors were held constant. Note that all CO₂ information presented in Figures 2-6 was collected with a simulated mouth opening of 20%, while Table 1 includes CO₂ information collected at a simulated mouth opening of 0%. Reducing the simulated mouth opening from 20% to 0% caused a greater rise in CO₂ inhalation for the dual-prong cannula than for the single-prong cannula when all other factors remained constant.

Table 1.

CO₂ flush results for models with varying cannula geometry, therapy flow, and mouth open percent.

Therapy flow (L/min)	Mouth open percent (%)	Single-prong CO2 inhaled (mg)	Dual-prong CO2 inhaled (mg)
45	20	2.06	2.19
35	20	2.20	3.09
27	20	2.55	4.45
21	20	3.04	5.67
12	20	4.73	7.34
5	20	7.58	N/A
45	0	2.75	6.95

Single-prong CO₂ inhaled refers to the mass of CO₂ inhaled each breath cycle when therapy is administered via a single-prong cannula. Dual-prong CO₂ inhaled refers to the mass of CO₂ inhaled each breath cycle when therapy is administered via a dual-prong cannula.

Contours of instantaneous mass fraction CO₂ are shown in Figure 7, where mass fraction CO₂ ranges from 0 (shown in blue) to 0.07 (shown in red). Contours were collected from the right profile view, with the face directed toward the right side of the page, concurrently on three planes to capture a more complete view of the upper airway than any single plane could provide. Contours collected at three important timestamps in the breath cycle are shown in Figure 7 for both the single-prong and dual-prong cannula geometries. Peak exhalation is the moment in the breath cycle of the highest expiratory volume flow. Peak CO₂ is the moment at which the most CO₂ is entrained in the upper airway. The temporal value of peak CO₂ can change from breath to breath depending on minor variations in the gas mixing patterns. End-exhalation is the moment just before the breath cycle switches from exhaling to inhaling. The CO₂ remaining in the airway at the end-exhalation timestamp is available for re-inhalation. Note that the contours were collected in the right naris, which is the open naris for the single-prong cannula models.

Figure 7.

Contours of instantaneous mass fraction CO₂ collected at three timestamps throughout the expiratory phase of the breath cycle are shown. Peak exhalation is the timestamp at which the expiratory volume flow was maximum, peak CO₂ was the timestamp at which the most CO₂ was present in the airway, and end-exhale was the last timestep of the expiratory phase. The contours are collected from a right profile view and are collected on multiple planes to give the reader a better understanding of the flow throughout the airway. The therapy flow was 35 L/min for each scenario shown. The first row (Dual-Prong) shows contours collected from a model being administered therapy using a dual-prong cannula, and an animation of a complete breath cycle can be found in the supplemental material (Supplemental Video S1). The second row shows contours collected from a model being administered therapy using a single-prong cannula geometry, and an animation of a complete breath cycle can be found in the supplemental material (Supplemental Video S2). The contours were collected on planes ranging from the center of the airway to the center of the right naris (single-prong contours collected in the naris that was not directly receiving therapy flow).

Discussion

A previous study showed that an asymmetrical dual-prong cannula with one prong smaller than the other produced lower patient minute ventilation and work of breathing (inspiratory esophageal pressure time product) than a symmetrical dual-prong cannula. ¹² This study shows that a single-prong cannula can produce an equivalent reduction of CO₂ rebreathing at a lower flow than the tested dual-prong cannula, and the difference in CO₂ inhalation between the dual-prong and single-prong cannula geometries increases as the therapy flow decreases (Figure 6) or the simulated mouth opening decreases (Table 1). A therapy flow of 12 L/min, which was the minimum therapy flow tested with both cannula geometries (5 L/min was only tested with a single-prong geometry), resulted in the inhalation of 2.61 mg of additional CO₂ when using the dual-prong cannula. This amount of CO₂ is the same as rebreathing an additional volume of stale expiratory air that is equal to ∼18% of the total upper airway volume simulated in this study. The lower CO₂ inhalation at the same therapy flow also means that the same CO₂ inhalation can be achieved at a lower therapy flow with the single-prong cannula geometry. If the same CO₂ inhalation can be achieved at a lower therapy flow, this could potentially lead to higher patient comfort, and in turn higher patient compliance, as well as lower resource use.

The consistency of the data seen in Figure 2 highlights an important advantage of using CFD for this study. Using CFD, one can replicate the simulated patient airway, delivered therapy flow, and imposed respiratory cycle across tests and across breaths. This facilitated the isolation of variables such as cannula geometry and therapy flow setting during testing. This consistency also enhances confidence in the interpretation of results, as it eliminates the noise imposed by human variability. Investigators must also perform in-depth validation studies to ensure CFD is being utilized in a trustworthy manner. The authors provide a detailed analysis of the validation of the modeling methodology used in this study in a previous publication. ¹¹

A randomized crossover trial evaluated 26 patients with hypercapnic COPD using single-prong HFNC versus traditional dual-prong HFNC. The results demonstrated a comparable dyspnea relief at a median flow of 15 L/min with single-prong HFNC versus 25 L/min for dual-prong systems. Similar reductions in transcutaneous CO₂ and perceived dyspnea scores were noted for both interfaces. This represents significant oxygen conservation potential, making single-prong HFNC ideal for rural hospitals, transport, and home care settings. ¹⁰ These findings suggest that single-prong HFNC can provide equivalent clinical efficacy at substantially lower flows, improving resource efficiency without compromising patient outcomes.

In Figure 3, notice the lower residence times seen with the single-prong cannula geometry when compared with the dual-prong geometry. The expiratory flow has an easy escape route via the open right naris for the model being administered therapy with a single-prong geometry. The dual-prong geometry, on the other hand, obstructs flow trying to leave the right naris. This limits the ability of expiratory flow to leave the upper airway, therefore trapping CO₂-rich gas in the upper airway. This agrees with what is seen in Figure 7, where there is a greater buildup of CO₂-rich flow in the airway. The contours in Figure 7 are collected in the open naris for the single-prong geometry, meaning you would expect to see a large amount of CO₂-rich flow in the nasal passageway at peak exhalation and peak CO₂. However, it can also be seen that the CO₂-rich flow is successfully leaving the airway via the jet that can be seen evacuating the nasal passageways and entering the environment region. The dual-prong geometry, on the other hand, has much weaker CO₂ evacuation at the interface between the nasal passageways and the environment region. Some flow with a non-zero CO₂ concentration is successfully escaping the airway out the nares, but it is to a much smaller degree than for the single-prong geometry. This manifests in the contours seen at end exhalation, where the single-prong geometry has an indiscernible amount of CO₂ in the uppermost portions of the airway and the dual-prong geometry has a slightly higher level of CO₂ retention.

A reduction in ΔCO₂ is seen in Figure 5 at the beginning of the exhalation period for each therapy flow setting tested. ΔCO₂ even briefly drops to negative values for therapy flow settings of 35 L/min and 45 L/min. This phenomenon may be due to the right naris being filled with CO₂-rich expiratory flow during the early stages of exhalation when therapy is administered via a single-prong cannula geometry. After the initial filling of the right naris with expiratory flow, the CO₂ level quickly begins decreasing as the expiratory volume flow decreases. On the other hand, the dual-prong cannula may have greater initial resistance to the nares filling with expiratory flow (and in turn force more early expiratory flow out the partially open mouth). However, as the expiratory volume flow increases, the dual-prong therapy is unable to force the expiratory flow out the mouth quickly enough to account for the right nasal passageway being blocked by the cannula geometry and therapy flow.

Notice also in Figure 5 that the end-exhalation ΔCO₂ value is diminished at higher therapy flows, which suggests that the single-prong cannula may exhibit greater advantages at lower therapy flows. The shape of the transient ΔCO₂ signal is also changing as the therapy flow is decreased. In general, the peak ΔCO₂ value is increasing, and the time in the breath cycle of the peak ΔCO₂ value is shifting closer to end-exhalation (time of 2.5 s in Figure 5) as the therapy flow is decreased. However, there is also a significant change in the transient characteristics of the 12 L/min curve during the expiratory phase (∼1.25 to 2.5 s in Figure 5) when compared to all other tested therapy flows. Future work could be conducted to run additional models that would investigate more therapy flow settings in this range to learn more about this change in the transient characteristics of the curve. Note that this phenomenon, or the therapy flow at which the phenomenon occurs, may be dependent on many factors such as airway geometry, cannula geometries compared, and breath curve applied.

This simulation demonstrates that the reduction in CO₂ inhalation achieved by a dual-prong cannula can be achieved at a lower therapy flow with the single-prong cannula geometry for the scenarios tested. The ability to produce a therapeutic reduction of CO₂ rebreathing at a lower therapy flow can yield greater patient comfort, resulting in greater patient compliance, as well as lower resource use, which is helpful in settings that have a limited oxygen supply.

Limitations

This study included results from one airway geometry. The results would be more generalizable if additional airway geometries were considered. A potential extension of the study could include multiple airway geometries with varying characteristics such as size and health (nasal inflammation, airway obstruction).

This study includes results that were exclusively collected using CFD models, which have inherent risks if used improperly. The CFD methodologies used in this study were experimentally validated, and an in-depth analysis of this process is included in a previous study by the authors. ¹¹ Additional information regarding the validated CFD methodologies is included in the supplemental materials. The conclusions drawn from the CFD models discussed in this study could be used to inform the structure of future clinical studies.

Conclusions

The single-prong cannula resulted in more efficient clearance of CO₂-laden exhaled air than the dual-prong cannula when all other factors remained the same. The distinction between the two was larger as the therapy flow was decreased and the simulated mouth opening was decreased. Pathlines released at the moment in the breath cycle at which the simulated patient was exhaling with the greatest volume flow showed that the single-prong cannula resulted in a lower airway residence time for exhaled flow.

Supplemental material

Supplemental material

Supplemental Material

Supplemental Material - The effect of single-prong high-flow nasal cannula therapy on CO₂ clearance

Supplemental Material for The effect of single-prong high-flow nasal cannula therapy on CO₂ clearance by Robert P. Kacinski, Wayne S. Strasser, Jonathan B. Waugh in Respiratory Care Reports